Thej' anchor it firmly in the soil, and also 

 absorb material that is to help in the manu- 

 facture of food. It is the older roots that 

 have long since stopped absorbing that are 

 the chief anchors. How firm this anchor 

 age must be we can, perhaps, imagine when 

 we think of the strain produced by a 

 great crown of leaves swaying back and 

 forth in the wind. It is only a cyclone that 

 seems to be able to overthrow a sound tree, 

 and then it more commonl)' breaks its trunk 

 than uproots it. 



The very important work of absorbing is 

 given over to the very j^oung roots; in fact, 

 chiefly to those of this year, for new root- 

 lets must be put out each j-ear. These 

 roots can only absorb water, so that if they 

 are to get anything from the soil it must be 

 something that water will dissolve. In this 

 way the water is used as the carrier of soil- 

 material into the root. Just how this water 

 carrying soil-material gets into the root is not 

 easy to explain, for the root has no holes 

 to let it in, and it must pass through living 

 walls. That it does enter, however, every 

 one knows. It is evident, therefore, that 

 the root is supplying to the tree two kinds 

 of raw material for food manufacture ob- 

 tained from the soil, namely, water and soil- 

 material dissolved in it. 



But the tree does not obtain all its raw 

 material from the soil. A very important 

 material is taken from the air, the material 

 commonly called " carbonic acid gas," the 

 same material that we breathe out so abun- 

 dantly from our lungs as one of our body 

 wastes. This important material is taken 

 out of the air into the plant chiefly by means 

 of the leaves. Spread out as they are in 

 the air, the leaves are in the most favorable 

 position for doing this work. 



But where and how are these three kinds 

 of raw material manufactured into plant 

 food ^ The leaves are specially constructed 

 to be the chief seat of this food manufacture. 

 The carbon gas is received directly into these 

 manufactories from the air, but the water and 

 the soil-material are clown in the roots, and 



it is necessary for them to be carried to the 

 leaves. As a consequence, a "current " of 

 water containing soil-material ascends froci 

 the roots, through the stem, and is distrib- 

 uted through the branches to the leaves. 

 This movement is generally known as the 

 ' ' ascent of sap. ' ' The path of this move- 

 ment in the stem is through what is known 

 as the " sap wood," and it is this very fact 

 which gives to this region of the wood its 

 peculiar character. Just how the sap ascends 

 through the stem and reaches the leaves, no 

 one knows. All of our explanations have 

 proved unsatisfactory, and only those who 

 are not fully acquainted with the facts claim 

 to be able to explain it. 



When the sap reaches the leaves, the water 

 is no longer needed as a carrier of soil- 

 material. Some of it is needed in the manu- 

 facture of food, but by far the greater part 

 of it escapes from the leaves into the air by 

 a process which maj^ be called ' ' plant 

 evaporation." The amount of water thus 

 brought from the soil and poured out into 

 the air by active plants is very great; and 

 when we consider a forest at work, we can 

 hardly compute the vast amount of moi.sture 

 which it is constantly contributing to the air 

 during the growing season. 



The three kinds of raw material thus 

 brought together chiefly in the leaves are 

 there manufactured into plant food. On 

 account of this work the leaves have often 

 been spoken of as the ' ' stomachs ' ' of the 

 plant. This is a ver}^ incorrect and mislead- 

 ing illustration, for the work referred to is 

 not digestion such as a stomach is concerned 

 with, and, in fact, it is a process entirely un- 

 known in animals, and found only in green 

 plants. It is a wonderful process, which we 

 do iiot at all understand, but it consists in 

 taking this dead raw material from soil and 

 air and manufacturing out of it living mate- 

 rial. Not only does the food of the plant, 

 and hence its life, depend upon this process, 

 but all the life of the world, as we under- 

 stand it, depends upon it. We know at 

 least two prominent conditions of this pro- 



